In radio communication fields such as cellular phone systems and in computer-related fields, information is transmitted by utilizing high-frequency waves of at least 1 GHz, and such high-frequency transmitting products as coaxial cables and printed circuit boards, which are low in dielectric constant, are used in high-frequency transmission lines for information transmission. A polytetrafluoroethylene [PTFE] resin or a like fluororesin, which are low in dielectric constant, are used as a resin constituting such high-frequency transmitting products.
However, a fluororesin shows changes in dielectric constant as the temperature changes. For example, when a fluororesin is used as a material of outdoor radio communication antennas in cellular phone base stations and the like, a temperature of the outdoor antennas rises to about 80° C. in the summer daytime and the antennas show decreases in dielectric constant as compared with a case where they are at ordinary temperature, namely at about 25° C., with the result that the transmission line impedance lowers, which sometimes leads to such troubles as mismatching, decreases in transmission efficiency and changes in directivity of antennas.
An electrical substrate material comprising a fluoropolymer material and a silane-coated ceramic filler accounting for 55% by weight of the whole material (cf. e.g. Patent Document 1) and a electrical substrate composite material comprising a polymer matrix and a ceramic filler material comprising two specific ceramics (cf. e.g. Patent Document 2), for instance, have been proposed as a material for moldings excellent in the temperature stability of relative dielectric constant. However, these materials contain a ceramic material in addition to PTFE and therefore have problems in that relative dielectric constant and dielectric loss tangent also become increased.    [Patent Document 1] U.S. Pat. No. 4,849,284    [Patent Document 2] U.S. Pat. No. 5,552,210